Integrated circuit (IC) devices are typically tested after manufacture by sending electrical signals to the devices while the devices are in an elevated temperature for a period of time. Devices that fail to operate normally during such electrical stressing can be discarded, and it can be determined under what temperatures a device of a certain type can be expected to reliably operate. This process is referred to as burn-in. Multiple integrated circuit chips are placed on a burn-in board (“BIB”) that is similar to a computer add-on card, but typically larger. The BIB is a printed circuit board with receptacles for the IC devices. The BIB also includes printed circuit connections between pins of the IC chips and connectors of the BIB.
FIG. 1 is a block diagram of a typical prior art burn-in system. System 100 includes BIB 105. BIB 105 includes a number of devices under test (DUTs) 110. In typical testing applications, the BIB is placed in a burn-in oven chamber to subject the DUTs 110 to high temperature cycles. BIB 105 is electrically connected to responsive driver board 115. Driver board 115 contains electronics 120 including traces for power, ground, and control signals to be propagated to BIB 105. Driver board 115 has a fixed number of channels (trace that carries an electrical signal) 125. Some of the channels 125 are used for ground channels, supply voltage, and high frequency clocks. The remaining channels are used to transmit data between the driver board 115 and the DUTS 110 on BIB 105. The driver board 115 uses some channels to drive control signals to the DUTs 110 and uses others to monitor (read) the response of each DUT (test data output (“TDO”) signal) to determine if the DUT is failing or passing. Electronics 120 also contain firmware that controls the routing of each channel to determine if the channel is used for driving or monitoring. The driver board typically also contains firmware with the expected response values and can compare these values to the actual received TDO signal for each DUT. The driver board may then forward the failing/passing data to a processing system (not shown) that contains user interface software.
FIG. 2 is a perspective view of a prior art burn-in system 100. Backplane board 130 provides thermal insulation between the BIB 105 that goes into the hot chamber and the driver board 115 that does not. Backplane board 130 contains connector sets 135 and 140. Connector set 135 connects to connector set 136 of BIB 105 and connector set 140 connects to connector set 141 of driver board 115. In backplane board 130, connector set 135 directly connects to connector set 140 providing electrical channels 125 (not shown). Backplane board 130 may also contain additional connector sets such as connector sets 150 and 151 for interfacing additional BIB/driver board pairs.
The number of channels 125 limits the number of DUTs 110 that may be tested with monitoring on BIB 105 at a time. This limitation is not apparent when the control signals are being written to the DUTs 110 because when the DUTs 110 are receiving data it is practical to make their input channels common (i.e., the input pins are connected in parallel). Monitoring the output, however, requires each DUT to be on its own channel. For example, a number of channels may be needed to drive the control signals from the driver board 115 to the DUTs 110. This number is a fixed value regardless of how many DUTs are on the BIB 105. Each of the remaining channels may used to monitor a DUT—i.e., receive the TDO signal from a DUT. For example, a system having 72 channels, 21 channels may be used as ground channels, supply voltage, and high frequency clocks, leaving 51 channels available. Of these, 30 channels, for example, may be used to drive the control signals (of course the number of channels required to drive the control signals depends on the device to be tested and the test to be conducted). With 21 monitoring channels available to receive the TDO signal, the maximum number of DUTs that can be tested at a time is 21. This does not present a problem for larger, more expensive, IC devices (e.g., some microprocessors) because their size may limit the number that can be tested at one time in any case. For example, BIBs are typically of a standard size and the number of a certain type of IC device that can fit on the BIB may be less than the number of available channels for receiving the TDO signal. Moreover, relatively expensive devices may more easily absorb the costs of testing. The problem is evident for smaller, less expensive IC devices (e.g., ASICs and custom ICs) where more devices could fit on the BIB and the limited throughput adds significantly to the unit cost.